1. Field of the Invention
The present invention relates to a fuel hose for use as a fuel transportation pipe for transporting an automotive fuel such as a gasoline, an alcohol-containing gasoline (gasohol), an alcohol, hydrogen, liquified petroleum gas (LPG), compressed natural gas (CNG), light oil or dimethyl ether.
2. Description of the Art
To cope with more stringent regulations against vapor emission of automotive fuel gases in recent years, various types of low-permeability automotive fuel hoses have been investigated. Exemplary low-permeability fuel hoses hitherto proposed are those produced by employing polyester resins such as polybutylene naphthalate (PBN) and polybutylene terephthalate (PBT) which are less permeable to fuels. However, where a hose of a single layer structure is produced by employing such a polyester resin alone, the hose has poor flexibility because the polyester resin (PBN, PBT etc.) is highly rigid. Therefore, it is a common practice to laminate a thin polyester resin layer and a thermoplastic resin layer for production of a low-permeability fuel hose.
However, a polyester resin (PBN, PBT etc.) does not adhere well to other types of materials. Therefore, in the above hose, the polyester resin layer and the thermoplastic resin layer should be laminated by providing an adhesive layer therebetween, correspondingly complicating the production process. To this end, a hose has been proposed which includes an innermost layer of a thermoplastic polyester elastomer provided on the inner periphery of a polyester resin layer such as of the PBN or the PBT. Since the innermost layer and the polyester resin layer provided on the outer periphery of the innermost layer are both polyester-based, the innermost layer and the polyester resin layer can be laminated without the use of an adhesive by co-extruding the thermoplastic polyester elastomer and the polyester resin (e.g., PBN). However, the inventors of the present invention found, as a result of further studies on this hose, that the innermost layer of the thermoplastic polyester elastomer is unsatisfactory in sour gasoline resistance (resistance to a sour gasoline generated through oxidation of a gasoline) which is an important property required in hose applications for fuels.
In view of the foregoing, it is an object of the present invention to provide a fuel hose which is less permeable to automotive fuels and highly resistant to sour gasoline.
In accordance with the present invention to achieve the aforesaid object, there is provided a fuel hose which comprises at least one layer including an innermost layer comprising a thermoplastic polybutylene terephthalate elastomer containing a dimer acid moiety.
The inventors of the present invention conducted studies to determine the reason a hose which has an innermost layer composed of the thermoplastic polyester elastomer tends to be inferior in sour gasoline resistance, and discovered that a polyether contained as a soft segment in the thermoplastic polyester elastomer is liable to be eroded by a peroxide in the sour gasoline, thereby resulting in the deterioration of the hose. As a result of further research and development, the inventors found that where a dimer acid moiety is introduced into a thermoplastic polybutylene terephthalate (PBT) elastomer containing polybutylene terephthalate (PBT) as a hard segment to reduce the proportion of the soft segment (polyether) or to entirely replace the soft segment with the dimer acid moiety, the innermost layer is less likely to be eroded by the peroxide in the sour gasoline, whereby the hose tends to be free from deterioration by having an improved sour gasoline resistance. Thus, the present invention has been attained.